The invention relates to centering a boring head within a cylinder to be bored. Centering fingers are attached directly to the boring head to insure accurate positioning of the boring head within a cylinder of the type typically encountered in boring automotive motor blocks of original manufacture and reconditioning of motor blocks.
The machine tool industry which deals extensively with the automotive industry and the reconditioning of automotive motors, recognizes the constant need for centering devices adapted to produce accurate machine borings. The industry is confronted with the constant problem of precision boring auto-block cylinders and other cylindrical cavities. Accurately bored cylinders are necessary for the proper manufacture of motors. In new manufacture, the automotive block is typically cast and then bored to specific final dimensions. Also, in the large industry of reconditioning automotive and truck motors, there exists a constant need for accurately boring the cylinders of motor blocks. Without an accurate method of boring the old cylinders and reconditioning for reuse, these valuable parts would need to be simply discarded for new manufacture. A variety of solutions to the problem of producing accurate reborings and have been devised and put into practice.
Some of the prior art devices solve the problem of accurately centering a boring head by taking measurements from outside of the cylinder and attempting to position the boring head from measurements taking externally of the cylinder. Other prior art attempts to solve this problem by positioning the boring head with respect to the cylinder walls. Using cylinder walls as the reference point presents several problems. Accurate centering using this system can be difficult because the centering device is not permanently attached to the boring head. This presents problems because each time the boring head is moved and each time the centering device is applied to the boring head there is a chance for a slightly different positioning of the boring head within the cylinder.
Another apparatus for centering a boring head incorporates both the boring tool and the centering device in a single unit. Incorporation of the centering mechanism in the boring head tool carrier helps to insure accurate repeated centering of the boring head. An example of an apparatus of this type is illustrated in Canadian Patent Number 841317. Even this more useful and accurate method of centering, continues to present technical and physical problems to the industry. The space available for mounting such a centering device on the boring head is limited by the size of the cylinder to be bored. Because of this limited space in which to mount such a centering device, any such incorporation of the centering device on or in connection with the boring head tends to weaken the boring head. It is desirable to use a boring head which is as strong as possible to prevent any flexing of the head and tool, chattering of the spindle and bore head or similar variations which can be produced by a weak or flexible boring head.
Further, because of the limited space in which to mount a boring head, the prior art has provided mechanisms with a limited measuring range. Such centering devices have limited extension capabilities for application to a variety of cylinder sizes.
Another serious problem not totally solved by the prior art is fouling which occurs during the boring process. Cooling liquids, metal chips fine grindings and other debris is dislodged from the cylinder walls during the boring process. When centering devices are incorporated in the boring head, these centering devices tend to become fouled and therefore tend to lose operating efficiency. Fouling causes the problem of mechanical wear in the centering devices. The wear tends to be uneven so that the centering device loses accuracy and loses usefulness as a centering device. This of course requires repair of the centering fingers and possibly the boring head itself.